The controlling mechanisms which regulate production of inflammatory mediators by endotoxin stimulated murine macrophages are currently under investigation. Research has concentrated upon two important mediators, interferon and granulocyte-macrophage colony stimulating factor (CSF), and evidence has been obtained indicating that prostaglandins may serve a regulatory role in production of both mediators. Addition of indomethacin, a potent inhibitor of prostaglandin synthesis, to endotoxin-stimulated macrophage cultures has been shown to enhance interferon production and to elevate the colony stimulating activity of culture supernatant fluids. Work currently in progress is designed to determine if prostaglandins do indeed serve to regulate interferon and CSF production and if this controlling influence is mediated via cyclic nucleotides.